1. Technical Field
The present disclosure relates generally to an M-ary Phase Shift Keying (MPSK) demodulation apparatus and method and, more particularly, to an MPSK demodulation apparatus and method that determine a received symbol using a plurality of correlators in a wireless channel in which bandwidth is limited.
2. Description of the Related Art
Phase Shift Keying (PSK) is a transmission method that is chiefly used in a channel in which bandwidth is limited because its bandwidth efficiency is high, and is divided into Binary PSK (BPSK) and MPSK.
BPSK performs modulation and demodulation using a single frequency mixer. A modulation apparatus using BPSK uses a frequency, generated by its own frequency generator, as a carrier frequency. Furthermore, a demodulation apparatus using BPSK may use a coherent demodulation method that synchronizes and uses a carrier frequency and a phase from a received signal, or a non-coherent demodulation method that uses a frequency generated by its own frequency generator. In this case, although the coherent demodulation method imparts system performance that is superior to that of the non-coherent demodulation method, it is problematic in that complexity is required to recover carrier frequency and in that implementation becomes more difficult as carrier frequency increases.
In a low frequency communication environment, MPSK is required for bandwidth efficiency because the bandwidth used is narrow, and also a coherent demodulation method having excellent error performance is required. For example, Korean Patent Application Publication No. 10-2007-0050634 entitled “Apparatus and Method for improving Symbol Error Rate Performance of M-PSK System having Quadrature Error” discloses a technology that mitigates the degradation of symbol error rate attributable to quadrature error estimation and quadrature error during the demodulation of an M-PSK signal in a system to which an MPSK method has been applied.
MPSK uses a quadrature modulation and demodulation method that performs division into an I channel and a Q channel using two frequency mixers having a phase difference of π/2 and then performs modulation and demodulation. Although the quadrature modulation and demodulation method has the advantage of being implemented using two frequency mixers for I and Q channels regardless of the size of M, a more precise digital-to-analog convertor (DAC) and a more precise analog-to-digital convertor (ADC) are required as M increases.
Although a DAC can be implemented using a relatively simple level converter because a modulation apparatus performs conversion into a set size signal, a demodulation apparatus requires a more precise ADC. When a precise ADC is used, digital signal processing is facilitated. However, this case is disadvantageous in that a received signal must be amplified to a sufficient magnitude in order to convert an analog signal into a digital signal, noise figure (NF) increases in response to the degree of amplification, and also quantization noise occurs during a signal conversion process, so that signal to noise ratio (SNR) and system performance may be degraded.
In an MPSK demodulation apparatus, noise has Additive White Gaussian Noise (AWGN) characteristics. AWGN noise is problematic in that it increases in accordance with the bandwidth used, temperature and current consumption and, thus, degrades SNR.